People With Horns II

The most significant potential link between Ico and Shadow in plot terms is Wander's appearance when he is possessed by Dormin. When the sixteen segments of Dormin finally recombine in Wander it significantly changes his appearance, and these changes include the growth of a pair of horns reminiscent of those borne by Ico and those like him. This connection is further strengthened by the fact that when Wander is killed, Dormin turns his body into a giant version of the Spirits which pursue Ico and Yorda; the Spirits that the people with horns in apparently become after death. That Wander gains these horns and then becomes a very similar kind of Spirit shows that what he goes through is closely related to the curse which afflicted the people with horns.

The Ico analysis strongly suggests that the particular trait which set the people with horns apart from everyone else, which gave them the horns, made them useful to the Queen, and resulted in them becoming Spirits, is some aspect of Dark Magic they have inherited. That Wander gains a similar appearance when he is possessed by a similar power supports this conclusion. Furthermore, it has the potential to tell us more about this 'trait'.
Taking Ico alone, we could only speculate that the trait that was passed down to and manifested in the people with horns was Dark Magic. Seeing what being possessed by Dormin did to Wander in Shadow, it is now basically certain that it is the presence of Dark Magic that sets the people with horns apart. It also tells us something more specific - that this Dark Magic is related to Dormin in particular. The horns that mark those tainted by Dark Magic could be a random reaction, except that Dormin itself bears the same horns, and those horns are the only more than superficial change to Wander. The horns are therefore not only a mark of Dark Magic, but a mark of Dormin's power in particular.

A question this leaves open is whether Dark Magic itself is a power which simply exists, or is Dormin's power in particular. Having tied the Spirits in Ico together with the one in Shadow, it is conceivable that Dormin is the direct source of all Dark Magic in the world, or at the very least, all that we have seen. This idea also fits in with the image of Dormin as a powerful figure rather than just another Spirit.
However, we must also consider the Queen and Yorda's dark form. While all the lesser Spirits in Ico, and Dormin, and Wander are all marked with horns, neither Yorda nor the Queen are, despite being Dark Beings. Furthermore, even some of Dormin's own manifestations are humanoid and yet feature no horns. Since these various beings do not bear the mark of Dormin and yet are Dark Magic in nature, we must conclude that Dormin is just a particularly powerful manifestation of Dark Magic, not the source of it.
Another conclusion is that these horns do not in fact represent Dormin as a whole - rather they mark the power of the sealed component. It is the greater body of Dormin which bears these horns, the lesser humanoid manifestations do not. It is also the presence of this greater power which causes the change in Wander. Thus the horns must represent the power in this particular manifestation of Dormin, which is so powerful that it not only altered Wander, but caused the mark to be passed down. For the direct link between Shadow and Ico is of course the infant at the end, who also bears the horns, just as Ico did when he was born.

One question which I did not ask in the original section on the people with horns is where they originated, where this trait originally came from. The infant at the end of Shadow offers an answer to this question. Now that we know the true meaning of the horns they bear, it was obviously some interaction with Dormin which created the first such person.
How exactly this relates to the people with horns referenced in Ico is unknown. It is unlikely that Wander is the first such person. As I will discuss in greater detail elsewhere, the Forbidden Land and the Fortress were apparently built by the same people, and were thus probably around the same time period. The Fortress contains reference to the people with horns, which means that they must have existed before the events of Shadow. Since we know the horns mark the presence of Dormin's power, this means that something similar to what happens to Wander must have happened in the past. That original spread of its power may even have been part of the motivation for sealing it away.
As for how the infant may relate to Ico, this may answer the question of where Ico's line in particular came from. Just as it is obvious that the Fortress and Forbidden Land were built in the same era, Ico and Shadow are also set in roughly the same era, featuring similar peoples. So where did the people with horns in this time come from? It may be a line which survived since the days of the Fortress, although the original 'People with Horns' section suggests that the Ancients were trying to stop exactly that. Another possibility is that Ico's line are all direct descendants of the infant, that the resurgence of the people with horns is Wander's doing.
There is nothing in particular to support either of these ideas. However, I would lean towards the latter simply because the birth of a new person bearing the taint of Dormin is something we know for certain, and since we know so few things for certain in either Ico or Shadow, I am inclined to lend it significant weight.